Stars in the very early stages of their formation are characterized by strong infrared excess and X-ray emission. We present the results of the survey of Orion A in both the infrared and X-rays obtained with the Spitzer and XMM/Newton observatories. We study the spectral-energy distribution class of the young stellar object (YSO) population using infrared colors from 2mass and Spitzer (IRAC and MIPS) and by means of X-ray fluxes, luminosities and plasma temperatures. We discuss clustering properties and spatial segregation among different infrared YSO classes to trace their formation history.

Free energy stored in the magnetic field is the source that powers solar and stellar activity at all temporal and spatial scales. The energy released during transient atmospheric events is contained in current-carrying magnetic fields that have emerged twisted and may be further stressed via motions in the lower atmospheric layers (i.e. loop-footpoint motions). Magnetic reconnection is thought to be the mechanism through which the stored magnetic energy is transformed into kinetic energy of accelerated particles and mass flows, and radiative energy along the whole electromagnetic spectrum. This mechanism works efficiently at scale lengths much below the spatial resolution of even the highest resolution solar instruments; however, it may imply a large-scale restructuring of the magnetic field inferred indirectly from the combined analysis of observations and models of the magnetic field topology. The aftermath of magnetic energy release includes events ranging from nanoflares, which are below our detection limit, to powerful flares, which may be accompanied by the ejection of large amounts of plasma and magnetic field (so called coronal mass ejections, CMEs), depending on the amount of total available free magnetic energy, the magnetic flux density distribution, the magnetic field configuration, etc. We describe key observational signatures of flares and CMEs on the Sun, their magnetic field topology, and discuss how the combined analysis of solar and interplanetary observations can be used to constrain the flare/CME ejection mechanism.

Determining the kinematics of the dwarf Spheroidal galaxies (dSph) satellites of the Milky Way (MW) is crucial to estimate the mass of our galaxy, to understand its formation process and that of its satellites, to explain the origin of stellar streams in the MW's halo that seem to be related to these satellites, and to understand the role of tidal interactions in the evolution and star formation history of low mass galaxies and of the halo of our Galaxy. In what follows we briefly explain a ground-based astrometric project that will have an impact on these issues, and present some preliminary results.

In recent years, a series of papers (Kroupa & Weidner 2003, Weidner & Kroupa 2004, Weidner & Kroupa 2005 and Weidner & Kroupa 2006, WK06 from now on) have proposed that the stellar content of an entire galaxy may not be well described by the same initial mass function (IMF) that describes the distribution of stellar masses in the star clusters, where these stars form. The reason is that star clusters also form with a cluster mass function (CMF), which is a power law with a power law index of ~−2. If the lowest mass clusters are of masses smaller than the physical upper mass limit for stars they will be deficient in high mass stars. Therefore, if the stellar content of all clusters is added together, making up the Integrated Galactic Initial Mass Function (IGIMF), the distribution of stellar masses may be steeper at the high mass end, depending on the exact shape of the CMF.

Massive spectroscopic surveys like the SDSS have revolutionized the way we study AGN and their relations to the galaxies they live in. A first step in any such study is to define samples of different types of AGN on the basis of emission-line ratios. This deceivingly simple step involves decisions on which classification scheme to use and data quality censorship. Galaxies with weak emission lines are often left aside or dealt with separetely because one cannot fully classify them onto the standard star-forming, Seyfert, or LINER categories. This contribution summarizes alternative classification schemes which include this very numerous population. We then study how star-formation histories and physical properties of the hosts vary from class to class, and present compelling evidence that the emission lines in the majority of LINER-like systems in the SDSS are not powered by black-hole accretion. The data are fully consistent with them being galaxies whose old stars provide all the ionizing power needed to explain their line ratios and luminosities. Such retired galaxies deserve a place in the emission-line taxonomy.

We investigate the origin of the color-magnitude relation (CMR) observed in cluster galaxies by using a combination of a cosmological N-body simulation of a cluster of galaxies and a semi-analytic model of galaxy formation. The departure of galaxies in the bright end of the CMR with respect to the trend defined by less luminous galaxies could be explained by the influence of minor mergers.

A large fraction, between 10 and 25%, of very metal-poor stars in the Galactic halo are carbon-rich objects, with enhancements of carbon relative to iron exceeding a factor 10. The majority of these carbon-enhanced metal-poor (CEMP) stars show enhancements of heavy s-process elements and have been found to be spectroscopic binary systems. Many of their properties are well explained by the binary mass transfer scenario, in which a former asymptotic giant branch (AGB) companion star has polluted the low-mass star with its nucleosynthesis products. The same scenario predicts the existence of nitrogen-rich metal-poor (NEMP) stars, with [N/C] > 0.5, from AGB companions more massive than about 3 solar masses. In contrast to CEMP stars, however, such NEMP stars are very rare. Recent studies suggest that the high frequency of CEMP stars requires a modified initial mass function (IMF) in the early Galaxy, weighted towards intermediate-mass stars. Such models also implicitly predict a large number of NEMP stars which is not seen.

Murray & Chiang (1997) developed a model wherein broad emission lines come from the optically thick base of a rotating, outwardly accelerating wind at the surface of an accretion disk. Photons preferentially escape radially in such a wind, explaining why broad emission lines are usually single-peaked. Less well understood are the observed shifts of emission-line peaks (from 1000 km s−1 redshifted to 2500 km s−1 blueshifted in C iv, with an average 800 km s−1 blueshift).

Sulfur abundances are derived for a sample of ten B MS star members of the Orion association. The analysis is based on LTE model atmospheres and non-LTE line formation theory by means of spectrum synthesis analysis of Sii and Siii lines. The abundance distribution obtained for the Orion targets is homogeneous within the errors in the analysis: A(S)=7.15±0.05. This abundance result is in agreement with the solar value and with results for the Orion nebula. The sulfur abundances for Orion combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of −0.037±0.012 dex Kpc−1.

We have obtained high-resolution VLT/FLAMES spectra of a number of giants in the LMC cluster Hodge 11 and the surrounding field. We present results of a detailed model-atmosphere abundance analysis for a variety of elements, including Fe, Ca, Ti, Si, Sc, Ni and Cr.

We present results from statistical analysis of the largest quasar surveys currently in existence: the Sloan Digital Sky Survey (SDSS), the 2dF QSO Redshift Survey (2QZ), and the 2dF-SDSS LRG and QSO (2SLAQ) Survey. The quasar luminosity function shows highly significant (>99.9%) evidence of downsizing: the number density of faint quasars peaks at lower redshift than bright quasars. We measure the distribution of quasar broad-line widths as a function of luminosity, particularly focusing on the Mg ii λ2799 line. There is a clear trend, such that more luminous quasars show less scatter in line width than fainter quasars. However, the scatter in line width for any given luminosity (particularly in the brightest objects) is so small that it challenges our current understanding of virial black hole mass estimates.

From high resolution spectra taken with the spectrograph FIES on the Nordic Optical Telescope, La Palma, we measure abundances of oxygen and α-elements in order to characterize stars which from their dynamical properties are suspected to have originated in disrupted satellites. We find that the chemical composition of investigated stars is homogeneous and distinct from Galactic disk dwarfs, which is providing further evidence of their extragalactic origin.

The fundamental physical parameters of open clusters are important tools to understand the formation and evolution of the Galactic disk and to test star-formation and evolution models. However, only a small fraction of the known open clusters in the Milky Way have precise determinations of distance, reddening, age, metallicity, radial velocity and proper motion. One of the major problems in determining these parameters lies in the difficulty to separate cluster members from field stars and to assign membership. We propose a decontamination method by employing 2mass data in the regions around the clusters NGC 1981, NGC 2516, NGC 6494 and M11. We present decontaminated colour–magnitude diagrams of these objects showing the membership probabilities and structural parameters as derived from King-profile fitting.

We present measurements of the EUV spectral irradiance we have obtained from radiance measurements with the SOHO Coronal Diagnostic Spectrometer, from 1997 to date. We discuss the contribution of the various regions of the Sun to the total EUV irradiance, and how they varied dramatically between the last two solar minima. These observations allow us to interpret spectral irradiance measurements in the EUV which have been available since 2002 with the TIMED mission. We also briefly discuss how changes in various activity indices compare with the EUV spectral variability, and the limitations of spectral modelling.

We explore the multiwavelength properties of three nearby starburst galaxies: NGC 3079, NGC 7673, and Mrk 08. We established that each of these galaxies has similar rest-frame far-ultraviolet (FUV) morphologies as Lyman-break galaxies (LBGs) at z ~ 1.5 and 4, when the age of the Universe was ~ 4.3 and ~ 1.6 Gyr, respectively. LBGs are at an important stage in galaxy evolution when the Universe had a peak in the star-formation-rate density. Many LBGs are primarily composed of star-forming clumps, i.e., stellar clusters, with a significant lack of older stellar populations. Here, we present the comparison of the spectral-energy distributions (SEDs) of three nearby starburst galaxies with those of typical LBGs. From our nearby sample, each object has been artificially redshifted to observe what the galaxies would look like at z ~ 1 to 4 in the rest-frame FUV. NGC 3079 is an edge-on Seyfert 2 galaxy. It has a bright bulge and is interacting with two other galaxies, with extended Hi only along NGC 3079. The redshifting process changes its appearance, so that at high z it looks like a chain galaxy with multiple knots of star formation and no bulge. NGC 7673 has extended Hi and the star formation is mostly within the inner optical region in the multiple star-forming clumps defining the galaxy morphology. In the FUV, the galaxy looks highly compact with little detail resolved. As it is artificially redshifted, the galaxy continues to look more spherical. Mrk 8 is a merging pair, with the two galaxies observable in the visible spectrum. It is classified as a Wolf–Rayet galaxy, which suggests a very young burst, and is composed of several large star-forming regions. The FUV image does not resolve the separate galaxies, and the appearance remains similar for each redshift. We use the Gini coefficient, M20, and the Sérsic index to quantify the morphologies. The SEDs of the objects have similarities with LBG stellar population models. Because these local galaxies can be studied in more detail, they act as a bridge between nearby observations of starburst galaxies and high-z starburst galaxies such as LBGs.

Globular star clusters generally have large cores, i.e., rc/rh (the ratio of core to half-light radii) exceeds 0.3 for more than 50% of the Galactic globular clusters. In the absence of a central heating source, dynamical models suggest that massive clusters will contract, typically on a timescale shorter than a Hubble time, and exhibit a compact core. To explain the disagreement between observations and theory, intermediate-mass mass black holes have been invoked to explain the core structure. Recent observations, however, have failed to definitively prove their existence in clusters. A new scenario, involving a natal kick given to white dwarfs may provide the required heating and help clusters avoid or delay core collapse.

People working on stellar populations can look forward to an exciting decade ahead. Investigations of stellar populations lie at the heart of the science cases being used to justify the development of upcoming telescopes and emerging instrumentation technologies. Examples abound, but I will focus on three case studies: (1) Wide field astronomy with upcoming ground-based and space-based survey facilities; (2) Adaptive optics, which has the potential to revolutionize our understanding of stellar populations in both nearby and distant galaxies; (3) The James Webb Space Telescope, which may well extend the reach of stellar population work to encompass the full range of the star-forming history of the Universe. However, most of these developments will require extensive advance preparation in order to be used effectively. The time to start that preparation is now (if not yesterday). Three areas which need urgent development are highlighted in these proceedings: (1) We need a wide-field high-resolution spectroscopic capability to augment wide-area imaging surveys; (2) We need a set of AO-friendly extragalactic deep fields in order to exploit upcoming AO-fed instrumentation; and (3) Existing tools for population synthesis modeling need to be extended in order to incorporate the effects of dust. Because the physics of dust creation and destruction is so complicated and uncertain, the latter capability sounds almost impossibly hard to develop, but in this talk I will argue that some simple approaches already exist that allow dust to be injected rather naturally into population synthesis models. I will show a concrete example where incorporation of dust into spectral synthesis models allows one to detect and characterize rate of formation of circumstellar disks at high redshifts.

The physical behaviour of methane and carbon dioxide clathrate hydrates, specific crystallographic ice crystals are of major importance for the earth and may control the stability of gases in many astrophysical bodies such as the planets, comets and possibly interstellar grains. Such models claim they provide an alternative trapping mechanism modifying the absolute and relative composition of icy bodies and can be at the source of late time injection of gaseous species in planetary atmospheres. However, there is a clear need to detect them directly. We provide in this study the laboratory recorded signatures of clathrate hydrates in the near to mid-infrared for astrophysical remote detection. These laboratory experiments will in a near future allow to follow the kinetic formation by diffusion in dedicated experiments, another important step to implement, to understand and model their possible presence in space.

We have undertaken CCD photometry in the eight-color Vilnius + I system for the open cluster IC 361 (l = 147.5°, b = 5.7°) located in the constellation of Camelopardalis. Based on multicolor data, estimates of distance moduli, foreground reddening and metallicity have been obtained for individual stars measured in the field of the cluster. This allowed us to eliminate most of the field stars and to identify the probable cluster members, from which we derived the true distance modulus (m − M)0 = 12.7 mag and metallicity [Fe/H] = −0.3 dex. The interstellar extinction is found to be nonuniform across the field, with values of AV ranging from 1.9 to 2.6 mag. A comparison of the color–magnitude diagrams with Padova isochrones yields (m − M)0 = 12.6 mag, or a cluster distance of 3.3 kpc, and an age of 1.0 Gyr. Therefore, IC 361 appears to be a mildly metal-deficient cluster of intermediate age, located as far as, or just beyond, the Perseus spiral arm.

Ultra-luminous infrared galaxies (LIR > 1012L⊙) are locally rare, but appear to dominate the co-moving energy density at higher redshifts (z > 2). Many of these are optically faint, dust-obscured galaxies that have been identified by the detection of their thermal dust emission in the sub-mm. Multi-wavelength spectroscopic follow-up observations of these sub-mm galaxies (SMGs) have shown that they are massive (Mstellar ~ 1011M⊙) objects undergoing intense star-formation (SFRs ~ 102–103M⊙ yr−1) with a mean redshift of z ~ 2, coinciding with the epoch of peak quasar activity. Furthermore, the presence of AGNs in ~ 28–50% of SMGs has been unveiled in the X-ray and near-IR. When both AGN and star-formation activity are present, long-slit spectroscopic techniques face difficulties in disentangling their independent contributions from integrated spectra. We have observed Hα emission from a sample of three SMGs in the redshift range z ~ 1.4–2.4 with the integral field spectrograph OSIRIS on Keck, in conjunction with Laser Guide Star Adaptive Optics. The spatially resolved, two-dimensional spectroscopic insight that these observations provide is the only viable probe of the spatial distribution and line-of-sight motion of ionized gas within these galaxies. We detect multiple galactic-scale sub-components, distinguishing the compact, broad Hα emission arising from an AGN from the more extended narrow-line emission of star-forming regions spreading over ~ 8–17 kpc. We explore the dynamics of gas in the inner galaxy halo to improve our understanding of the internal dynamics of this enigmatic galaxy population. We find no evidence of ordered orbital motion such as would be found in a gaseous disk, but rather large velocity offsets of a few hundred kilometers per second between distinct galactic-scale sub-components. Considering the disturbed morphology of SMGs, these sub-components are likely remnants of originally independent gas-rich galaxies that are in the process of merging, hence triggering the ultraluminous SMG phase.